Sheeting materials that have a graphic image or other mark have been widely used, particularly as labels for authenticating an article or document. For example, sheetings such as those described in U.S. Pat. Nos. 3,154,872; 3,801,183; 4,082,426; and 4,099,838 have been used as validation stickers for vehicle license plates, and as security films for driver's licenses, government documents, music media, playing cards, beverage containers, and the like. Other uses include graphics applications for identification purposes such as on police, fire or other emergency vehicles, in advertising and promotional displays and as distinctive labels to provide brand enhancement.
Another form of imaged sheeting, disclosed in U.S. Pat. No. 4,200,875, discloses the use of a plurality of transparent glass microspheres partially embedded in a binder layer and partially exposed above the binder layer, with a metal reflective layer coated on the embedded surface of each of the plurality of microspheres. Images are formed by laser irradiation of the sheeting through a mask or pattern. The images can only be viewed if the sheeting is viewed from the same angle at which the laser irradiation was directed at the sheeting. Thus, the image is only viewable over a very limited observation angle.
Another approach to making floating image sheeting, which operates over a wider observation angle, is disclosed in U.S. Pat. No. 6,288,842, in which a microlens sheet, typically an array of closely packed microspheres embedded in a binder layer and overlies a layer of photosensitive material. The image is written into the sheet by writing one point of the image at a time onto the photosensitive layer with a pulsed laser. This process is time consuming and expensive. In addition, the color of the floating image is determined by the color of the photosensitive material or the material surrounding the photosensitive layer and is, therefore, set at the time that the sheet is manufactured, rather than at the time the image is produced.
There remains, therefore, a need to improve the speed and reduce the cost of manufacturing optical sheets that demonstrate floating images, while at the same time maintaining wide observation angles and increasing the flexibility in the use of color in floating images.